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ItemLow-latency XPath Query Evaluation on Multi-Core Processors( 2017-01-04)XML and the XPath querying language have become ubiquitous data and querying standards used in many industrial settings and across the World-Wide Web. The high latency of XPath queries over large XML databases remains a problem for many applications. While this latency could be reduced by parallel execution, issues such as work partitioning, memory contention, and load imbalance may diminish the benefits of parallelization. We propose three parallel XPath query engines: Static Work Partitioning, Work Queue, and Producer- Consumer-Hybrid. All three engines attempt to solve the issue of load imbalance while minimizing sequential execution time and overhead. We analyze their performance on sets of synthetic and real-world datasets. Results obtained on two multi-core platforms show that while load-balancing is easily achieved for most synthetic datasets, real-world datasets prove more challenging. Nevertheless, our Producer-Consumer-Hybrid query engine achieves good results across the board (speedup up to 6.31 on an 8-core platform).
ItemA Comparison of Task Parallel Frameworks based on Implicit Dependencies in Multi-core Environments( 2017-01-04)The larger flexibility that task parallelism offers with respect to data parallelism comes at the cost of a higher complexity due to the variety of tasks and the arbitrary patterns of dependences that they can exhibit. These dependencies should be expressed not only correctly, but optimally, i.e. avoiding over-constraints, in order to obtain the maximum performance from the underlying hardware. There have been many proposals to facilitate this non-trivial task, particularly within the scope of nowadays ubiquitous multi-core architectures. A very interesting family of solutions because of their large scope of application, ease of use and potential performance are those in which the user declares the dependences of each task, and lets the parallel programming framework figure out which are the concrete dependences that appear at runtime and schedule accordingly the parallel tasks. Nevertheless, as far as we know, there are no comparative studies of them that help users identify their relative advantages. In this paper we describe and evaluate four tools of this class discussing the strengths and weaknesses we have found in their use. \